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A Molecular Precursor to Phosphaethyne and Its Application in Synthesis of the Aromatic 1,2,3,4-Phosphatriazolate Anion

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posted on 2016-05-12, 00:00 authored by Wesley J. Transue, Alexandra Velian, Matthew Nava, Marie-Aline Martin-Drumel, Caroline C. Womack, Jun Jiang, Gao-Lei Hou, Xue-Bin Wang, Michael C. McCarthy, Robert W. Field, Christopher C. Cummins
Dibenzo-7-phosphanorbornadiene Ph3PC­(H)­PA (1, A = C14H10, anthracene) is reported here as a molecular precursor to phosphaethyne (HCP), produced together with anthracene and triphenylphosphine. HCP generated by thermolysis of 1 has been observed by molecular beam mass spectrometry, laser-induced fluorescence, microwave spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. In toluene, fragmentation of 1 has been found to proceed with activation parameters of ΔH = 25.5 kcal/mol and ΔS = −2.43 eu and is accompanied by formation of an orange insoluble precipitate. Results from computational studies of the mechanism of HCP generation are in good agreement with experimental data. This high-temperature method of HCP generation has pointed to new reaction chemistry with azide anion to produce the 1,2,3,4-phosphatriazolate anion, HCPN3, for which structural data have been obtained in a single-crystal X-ray diffraction study. Negative-ion photoelectron spectroscopy has shown the adiabatic detachment energy for this anion to be 3.555(10) eV. The aromaticity of HCPN3 has been assessed using nucleus-independent chemical shift, quantum theory of atoms in molecules, and natural bond orbital methods.